STRUCTURAL GEOLOGY OF THE QUSEIR AREA, RED SEA COAST, EGYPT BY DAVID C. GREENE

Red

Gebe l Ambog i

Block

Sea

('I 0

0

U'_..

o,..

26°05 '

. " .

. .... .

South eas t

Block

1 N

1 km

34°15'

'----'

CONTRIBUTION NO. 52 DEPARTMENT OF GEOLOGY 8i GEOGRAPHY UNIVERSITY OF MASSACHUSETTS AMHERS~MASSACHUSETTS

STRUCTURAL GEOLOGY OF THE QUSEIR AREA, RED SEA COAST, EGYPT

By David Carl Greene

Contribution Number 52 Department of Geology and Geography University of Massachusetts Amherst, Massachusetts August, 1984

Prepared in cooperation with the Earth Sciences and Resources Institute of the University of South Carolina

..... ..... .....

1 N

Figure 1. Return-beam vidicon image of the Quseir region. Precambrian basement is dark in color, with large granitic bodies slightly lighter. Platform sediment blocks and the Red Sea coastal plain are very light in color. The large block on the west is Gebel Duwi; the study area comprises the eastcentral portion of the image (see fig. 3).

ABSTRACT

The Quseir area of the Red Sea coast of Egypt (26° Ol'N

lat.

to

26°

lO'N

lat.)

includes

three

major

lithologic groups: (1) a late Precambrian basement complex consisting of highly deformed volcanics and volcanogenic sediments metamorphosed to lower greenschist f acies;

( 2)

Cretaceous to early Eocene platform sediments consisting of up to 600 m of well-bedded sandstones, limestones; plain

shales and

and (3) Miocene to Recent Red Sea coastal

sediments

consisting

of

fanglomerates,

marls,

evaporites and calcareous reef deposits. The Precambrian volcano-sedimentary units appear to have been deposited in an oceanic island-arc environment. Subsequent deformation by predominantly northeast compression resulted in development of a tight synform plunging approximately 60° toward S40E,

axial planar

regional foliation trending N35W, and a quartz vein set trending N45E.

Major granitic intrusions were syn- to

post-tectonic. The unconformably overlying platform sediments are exposed as east-dipping tilted blocks and down-faulted inliers within the Precambrian basement.

Emplacement and

preservation resulted from 300 m to 1 000 m of motion on a system of west-dipping,

iv

north- to northwest-trending

normal faults,

and from lesser motion on subsidiary east-

dipping faults. The coastal plain sediments,

deposited at the margin

of the developing Red Sea rift, thicken and dip eastward toward the rift axis.

Abrupt vertical and lateral f acies

variations reflect syn-sedimentary faulting, coralline reef growth, and local variations in sediment supply. Detailed

study

of

Tertiary

fault

motions

has

documented a pattern of early strike-slip faulting with subsequent dip-slip reactivation.

Rignt-lateral strike-

slip faults trending N20W and left-lateral faults trending N60E form a conjugate system, indicating N20E compression in the Quseir region in middle Eocene to Oligocene time. North- to northwest-trending faults were reactivated in late Oligocene to early Miocene time as west-dipping normal faults, resulting in tilting and emplacement of the platform sediment inlier blocks. Uplift and erosional truncation of fault blocks in the early Miocene culminated in development of a terminal erosion surf ace termed the mid-Tertiary pediplain.

A

second period of rift marginal uplift, active in postPliocene time, has elevated the mid-Tertiary pediplain and exposed Quaternary wadi and reef terraces on the coastal plain.

v

A five-phase Cenozoic evolution of the Red Sea rift in the Quseir region is proposed.

Phase 1:

north-

northeast compression in middle Eocene to Oligocene time; Phase 2: in

continental margin extension and block rotation

late Oligocene or early Miocene time;

Phase 3:

formation of a proto Red Sea in middle Miocene time; Phase 4: quiescence during the late Miocene; and Phase 5: sea

floor spreading, active from the Pliocene to the present.

vi

TABLE OF CONTENTS

ABSTRACT

iv

Chapter

Page

I. INTRODUCTION

1

Purpose of Research . . . Description of Quseir Region . Previous Work . . . . . . Acknowledgements . . . . . . .

.

II. REGIONAL GEOLOGIC SETTING Introduction . . . . . . . . . . Precambrian Basement Complex . . Eastern Desert . . . Arabian-Nubian Shield . Platform Sediments . . . . Red Sea Sediments Mediterranean Sediments III. STRATIGRAPHY OF THE QUSEIR AREA Precambrian Basement Complex . . . . . . . Introduction Present Study . . . . . . . Metavolcanic/metasedimentary group mafic volc~nic unit (vm) porphyritic volcanic unit (vp) mixed sediments and volcanics unit (sv) . . . . . . . . . . silicic volcanic unit (vs) ... . fine sediment unit (sf) .. . mafic volcanic flows unit (vf) . . . conglomerate unit (sc) ... . intermediate volcanic unit (vi) . . white quartz porphyry unit (vw) . grey phyllite unit (sp) . . . . . . schistose phyllite unit (ss) Subvolcanic/plutonic group . . . . older granite (og) post-Hammamat felsite (ph) younger granite (yg) dikes and veins vii

1 3 5 8 11 11 11 11 13 17 17 18

19 19 19 22 23 23 24

25 26 26 27 27

28 28 28 29 29 30 30 30 34

TABLE OF CONTENTS (Continued) Chapter III.

Page

STRATIGRAPHY OF THE QUSEIR AREA (cont.) Late Mesozoic/Early Cenozoic Platform Sediments Nubia Formation . Quseir Formation Duwi Formation Dakhla Formation Tarawan Chalk . Esna Shale Thebes Formation Nakheil Formation .

IV.

35 35 40 41 43 43

44 44 46

Red Sea Coastal Plain Sediments Gebel el Rusas Formation Evaporite Formation . Gasus Formation Quaternary Back Reef Deposits Reef Terraces . Wadi Terraces . Active Wadi Alluvium Fringing Reef Complex

47 47 52 56

Erosion Surfaces . Introduction Pre-Cretaceous Erosion Surface Mid-Tertiary Erosion Surface . .

58 58 59 59

54

57

58 58 58

STRUCTURE OF THE QUSEIR AREA .

61

Precambrian Basement Complex Folding . Faulting Foliation . Dikes and veins .

61 61 61 62 64

viii

TABLE OF CONTENTS (Continued) Chapter

Page

IV. STRUCTURE OF THE QUSEIR AREA (cont.) Late Mesozoic/Early Cenozoic Platform Sediments Introduction . . . . Gebel Ambagi Area Gihania Valley Southeast Coastal Block . . Central Nubia Valleys . . Details of Fault Movements Summary and Interpretation . . . .

67 67 69 69 74 74 75 86

89 89 89

Red Sea Coastal Plain Sediments Gebel el Rusas Formation Ambagi reef . . . Isewid reef . . Rusas/PC reefs Remnants on the mid-Tertiary Erosion Surf ace . Other outcrop areas Evaporite Formation . Gasus Formation . . . Quaternary Sediments

102 103 103 105 109

Erosion Surfaces .

110

V. PHANEROZOIC REGIONAL TECTONICS . Introduction . . . . . . The Red Sea Rift System Morphology Stratigraphy Axial Trough Main Trough Summary . . . . Geology of Saudi Arabia Introduction Stratigraphy Structure Geology of the Sinai

lX

.

97 97

114 114 114 115 116 117 118 123 126 126 126 129 130

TABLE OF CONTENTS (Continued) Chapter

Page

VI. EVOLUTION OF THE RED SEA RIFT

132

Relation of Observed Local Tectonics to the Evolution of the Red Sea Rift Introduction . . . . . . Origin of Main Trough Red bed sediments Two phase extension . . Rift development Transverse faulting Recent uplift . .

140

VII. GEOLOGIC HISTORY OF THE QUSEIR AREA Precambrian Geologic History Phanerozoic Geologic History . Erosion of Precambrian Platform sediment deposition North-northeast compression . Continental Margin Extension Formation of proto Red Sea Quiescence Sea floor spreading REFERENCES .

132 132 132 133 134 136 137 138

.

140 142 142 146 146 147 148 148 149 150

x

ILLUSTRATIONS Plate

1.

Precambrian geology of the Quseir area

2.

Phanerozoic geology of the Qusseir area

3.

Cross sections of the Quseir area [plates in back pocket]

Figure

Page

1.

Landsat image of the Quseir region

2.

Index map of Egypt showing study area

2

3•

Geographic map of Quseir region

4

4.

Index map of Quseir region showing location of mapped areas .

9

lll

5.

Generalized geologic map of Egypt

12

6.

Generalized map of the Arabian-Nubian Shield .

14

Cross section of the Precambrian basement in the area of the el Isewid synform prior to regional deformation

20

Photograph of the Precambrian basement showing the Post-Hammamat Felsite . . . .

31

Stratigraphic column of the Mesozoic/Cenozoic platform sediments in the Quseir area .

36

Stratigraphic column of the Red Sea coastal plain sediments in the Quseir area .

48

Foliation in the Precambrian basement, Quseir area

63

Fracture cleavage in the Precambrian basement, Quseir area

65

7.

8.

9.

10.

11. 12.

xi

ILLUSTRATIONS (Continued) Figure

Page Orientations of (a) felsite dikes, (b) quartz veins in the Precambrian basement .

66

Faulted inlier blocks of platform sediments

68

15.

Photograph of the Gihania block

71

16.

Cross sections of Gihania block (A-B), Nubia Valley (C-D), and south Nubia valley (E-F) .

72

17 .

Detail map of Nubia Valley

76

18.

Orientations of (a) fault planes and (b) slickensides of Tertiary faults

78

Photograph showing dip-slip slickensides superimposed on strike-slip slickensides .

79

Orientations of slickensides from faults with two movement directions .

80

Fault plane and slickenside orientations of Tertiary strike-slip and oblique-slip faults with right-lateral motion . . . .

82

Fault plane and slickenside orientations of Tertiary strike-slip and oblique-slip faults with left-lateral motion . .

83

Sigma 1 orientations of Tertiary strikeslip and oblique-slip faults .

84

Tertiary stress systems in the Quseir area .

85

25.

Coastal plain reef complexes

90

26.

Map showing Red Sea coastline during middle Miocene time ....... .

91

13.

14.

19. 20. 21.

22.

2 3.

24.

xii

ILLUSTRATIONS (Continued) Figure

Page

27.

Detail map of the Ambagi reef complex

93

28.

Fault interactions in the Ambagi reef area .

94

29.

Cross sections of the Ambagi reef

96

30.

Photograph of the Rusas/Precambrian reef complex. .

99

Photograph and cross section of the Rusas/Precambrian reef complex . .

100

32.

Cross section of the Gasus reef complex

107

33.

Structural contour map of the Quseir region .

112

31.

TABLES Table Correlation of Cretaceous and Tertiary sediments in the Red Sea Region

128

2.

Precambrian history of the Quseir area .

141

3.

Phanerozoic history of the Quseir area

143

1.

Xlll

C H A P T E R

I

INTRODUCTION

Purpose of Research

The Red Sea Rift System includes one of the most recently rifted continental margins in the world.

It is a

region of fundamental importance for the study of the processes

of

rifting

and

continental

break-up.

The

northeastern margin of the Red Sea has been much studied in the past decade, most notably by the various missions associated with the Saudi Arabian Deputy Ministry for Mineral

Resources

(Brown,

1970;

Davies,

1980,

1981;

Hadley et al., 1982; Schmidt et al., 1982). Substantial oceanographic work has been completed within the Red Sea basin (Degens and Ross, Ross, 1977).

1969;

Whitmarsh et al.,

1974;

However, the Egyptian side of the Red Sea

has received much less attention due to difficulties of access and the smal 1 number of workers in the region.

The

purposes of this study are: (1) to provide geologic maps (plates 1 and 2) and detailed structural information for an area of the western margin of the Red Sea in Egypt, (2) to correlate these data with structural information from other workers in

Egypt and

Saudi Arabia,

examine the implications of these

and

to

data for the tectonics

and development of rifting in the Red Sea region. 1

( 3)

2

MEDITERRANEAN

.·.·.

SEA

-'\~SRA EL \ c..

\

'.·1· :.u::J 0 RDA N

··".::ARABIA

28°

26°

v--

Study

I

Quena ·.:: ·

Area l - "

\RED ·:.:. ...

"'Aswan

24°

SEA

·

100 km

EGYPT 3

Figure 2.

o0

_,

__ --- -- - -- 32SUOAN

3 4o

-3 6°

Index map of Egypt showing study area.

3

Description of Quseir Region The

study

area

is

situated

in

Egypt,

on

the

southwestern shore of the Red Sea, between 26° 01' and 26° 10' north latitude and 34° 09' and 34° 19' east longitude (figs.

1 and 2).

It is 140 square kilometers in area,

bounded by Wadi Quseir el

Qudeim on the north,

Wadi

Nakheil and Wadi Beda el Atshan on the west, an east-west line approximately 4 kilometers south of Wadi el Isewid on the south, and by the Red Sea on the east (fig. 3).

The

only permanent settlement in the region is the town of Quseir, a small fishing and phosphate-mining community with a population of about 15 000(?). Access to the area is generally adequate; a paved road runs north-south along the coastal plain, and another passes westward to Quena and Luxor in the Nile Valley. Most of the major wadis are passable in a four-wheel-drive vehicle,

and

many

have

remnants

of

constructed for phosphate exploration.

former

tracks

Scattered anti-

tank mine fields, and the use of the area south of Quseir as an artillery range, make access to the coastal plain somewhat more difficult. The climate of the region is extremely arid, with rainfall averaging less than 1 cm. per year, and daytime

RED SEA

,..--

Main Raad

,,..>---

Wadi Course

~

Topographic Contour

Contour Interval = 50 meters

0

I

2

3

KM

4

~

Figure 3. Geographic map of Quseir region. This study covers the eastern half of the region, a parallel study by M. Valentine covers the western half of the region. (Modified from Valentine, in preparation).

"""

5

temperatures averaging 20° to 30° Celsius (Cohen, 1973). Vegatation is sparse, consisting of scattered small bushes and isolated acacia trees restricted to the major wadis. The only permanent water in the area is

a brackish spring

which occurs in the narrowest part of Wadi Ambagi,

where

it crosses a ledge of the Precambrian basement. In general, the area consists of a flat coastal plain with uplifted, west-dipping plateaus of middle to late Tertiary sediments related to the Red Sea, and an elevated inland region.

The inland region has a rugged topography,

with several hundred meters of relief developed on highly deformed Precambrian basement, and local steeply tilted fault blocks of Cretaceous to Eocene platform sediments. Several Arabic words are commonly used in the text: gebel=mountain, bir=well.

wadi=dry stream course or valley,

and

The word "isewid" means black, thus Wadi el

Isewid is "black valley".

Qudeim means old, and Quseir el

Qudeim is "old Quseir", the original site of the port of Quseir and an important trading post in Roman and medieval Islamic times.

Previous Work

Much of the early work on the geology of Egypt is summarized

by

Said

(1962)

in his

excellent book The

6

§.~S2.l.S2..9.Y

Qf

include the

~.9.Y.12!..

Cur re n t 1 y a v a i 1 ab 1 e

§.~S2.l.S2..9.ic ~~2

Qf

~.9.Y2!.

g e o 1o g i c

(Egyptian Geological

Survey and Mining Authority, 1981), and the

Qf

!.~~ Q~~~~ QU~QE~ng_.!_~

maps

§.~S2.l2.9.i~ ~~

(ibid, 1978) which includes the

Quseir region. An extensive study of the Precambrian basement rocks of the northern Eastern Desert of Egypt was published by Schurmann (1966).

More recent work on the Precambrian

rocks of the Eastern Desert has been carried out by Akaad and Noweir ( 1979),

who published a detailed stratigraphy

for an area between latitudes 25° 35' and 26° 30' N; by Dixon (1979) and Stern (1979) who studied the stratigraphy and geochemistry in the west-central Eastern Desert;

and

by Sturchio et al. (1983), who described the Meatiq Dome area west of Quseir.

Recent ideas on the tectonic

evolution of the Precambrian Shield are presented in Engel et a 1 . ( 1 9 8 0 ) and Ries et a 1 . ( 198 3) . Mapping and stratigraphic analysis of the Red Sea coastal-plain sediments has been undertaken by a number of workers, noteably El Akkad and Dardir (1966) in the area to the south of Quseir between Ras Shagra and Mersa Alam, and Issawi et al. (1971) in the area between Safaga (fig. 2) and Sharrn el Qibili.

More recently, Johnson (1977)

7

completed a detailed study of the Miocene Gebel El Rusas Formation. Most previous work in the Quseir region has been related to exploration and assessment of phosphate resources occurring in the Cretaceous Duwi Formation.

The

work resulted in a generalized regional geologic map at a scale

of

1:100

unpublished),

000

(El

Akkad

and

Dardir,

1965,

and numerous detailed maps and descriptions

of phosphate localities (El Akkad and Dardir, 1966; Issawi et al., 1968, 1969; Glenn, 1980). The first geologic map of the Quseir region to distinguish units within the Precambrian basement complex was El Akkad and Dardir's

11

Ge_S?.1_.S?.9-i£ !i.§.E _S?_f

!_b_~ ~Q.§..§.!.§.l

§.!!..i.!2 ~~!~~~.!!. Q_~_!!_.§__:_§_.§.f.§._g_.§_ !3..S?. ad .§..!!.s'.! Sh.§.!_!!! ~l ~a b..§.!..i", (1965, unpublished).

Subsequently El Ramly, drawing on

the work of El Akkad and Dardir, included the area in his "New Geological and

!'.!.§_12_

Southeastern

1 : 1 0 0 0 0 0 0 ) . The

11

for the Base!!!ent Rocks in the Eastern Deserts Q_~QlQ_g_i£

of

~_g_yp_!_ll

!i.§.E _S?_f

!_b_~

(1972,

Qe _!!_.§_

Q_~.§_s'.!_ r

scale a gg__l~

11

(Egyptian Geological Survey and Mining Authority, 1978; 1:500 000) is the most recent general geologic map of the region which includes the Precambrian basement complex. In the Quseir region, Trueblood (1981) has mapped the

8

Phanerozoic sediments in an area north of Quseir, Abu Zeid (in progress) is mapping the Precambrian basement in an area to the northeast, and Valentine (in progress) has mapped an area to the west of this study area (fig. 4). These adjoining maps are being produced at the scale of 1:40 000, and collectively provide relatively complete geologic coverage of the region.

In addition,

Richardson

(1981) has mapped the Mesozoic and Tertiary sediments in the region south of Quseir at a scale of 1:100 000. Acknowledgements This report is based on 3 months field work carried out in the spring of 1982.

Field work was supported by

the National Science Foundation through the Earth Sciences and Resources Institute at the University of South Carolina.

Dr. William H. Kanes, Director, and Dr. Steven

Schamel, Associate Director of the Institute, and Dr. E. M. El Shazley and Mr. Hafez Aziz of the Egyptian Project were all very helpful with many aspects of the project. Mr.

Hassan Abu Zeid was of great assistance in the field,

as were numerous members of the local staff. assisted with petrographic analysis, provided computer support.

B. A. Greene

and W. R.

Greene

9

33° 50' 26°30'

34°20' 0

26° 30'

10

KM

Quseir

26 °

34° .._

I/"_.,

'"

.

\'-1~· \ ::::..,1_ -

RED

_.-1

SEA

''-1

VALENTINE

LEGEND ~1yj~:;~.~jWadi

Alluvium

1 0

0

•o 0

• o•••

••

•

•

0 0

k

J

~

+

IE

0 0

• •

N•73

ti0 ci)0

.... .

• • ~ -~ ·.: • • • • •• • • o•

s

•

/

" N = 73

s

I 0

I 1

2

fi:··.\i~ 3 5'1.

Figure 23. Sigma 1 orientations of Tertiary strike-slip and oblique-slip faults. (a) Sigma 1 orientations from individual fault planes. Solid dots represent sigma 1 orientations from faults in main sets, open dots represent sigma 1 orientations from faults in minor sub-sets. (b) Contour plot of sigma 1 orientations from individual fault planes.

CXl .i:-.

Late Tertiary ta Re cent Stress System

Early Tertiary Stress System N N2.0W

N 0"1 • N2.o E

O" '5. N70W

N60E

..._

.......

.......

..._ ..._

w

E

~

C7 = vertlcot ..._©..._ 1

.......

..._ ..._ ..._

.......

O"-s

o-,

s

s

Figure 24. Tertiary stress systems in the Quseir area. (a) Pre-rifting N20E compressional phase, (b) Rift and post-rift N20E extensional phase. co Vl

86

1.

subsequent block tilting during the onset of northeast extension,

2. 3.

local variations in the stress field, and previous zones of weakness in the underlying Precambrian basement acting

to control

later

fault orientations. This stress system is indicative of an early phase of north-northeast compression (fig. 24a), active prior to the development of the present extensional stress regime associated with the opening of the Red Sea (fig. 24b). Summary and Interpretation.

In the Quseir region a stable

tectonic regime was disrupted sometime during late Eocene to

Oligocene

compression,

time

by the onset of north-northeast

producing regional uplift and the cessation

of sedimentation.

This was accompanied by the development

of a conjugate system of north- to northwest-trending right-lateral strike-slip faults and northeast-trending left-lateral faults. The

north- to

northwest-trending

fault

set

was

strongly affected by the northwest structural grain of the underlying Precambrian basement,

which accentuated

development of through-going faults, and in particular favored the development of faults trending northwest. The stress system,

however,

appears to have favored more

87

nearly north-south right-latera 1 faults,

and the results

of this interaction can be seen in the common segmented pattern

of

the

right-lateral

fault

set,

in

which

northwest-trending fault segments alternate with more northerly segments {e.g., the Gebel Atshan fault,

plate

2) •

Elements of the northeast-trending left-lateral fault set appear to control many of the transverse topographic features in the region, including the terminations of a number

of

the

fault

block valleys

in

the

south,

the

orientations of Wadi el Isewid and Wadi Quseir el Qudeim, and the orientation of the transverse topographic high upon

which

the

developed.

Pliocene

Garson

and

Gasus

Krs

reef

(1976)

structures are

identify

regional

transverse fractures averaging N60E in both Egypt and Saudi Arabia.

They suggest that major fractures of this

orientation Precambrian,

may

have

first

developed

during

the

a suggestion possibly supported by the N60E

fracture cleavage set noted in the Precambrian basement in the Qusei r area. A system

of

broad

folds

and

arches

developed

concurrently with the strike-slip faulting to the north of the

study

(Trueblood,

area,

in

1981).

approximately

N40W,

the

vicinity

These also

folds

of

Gebel

el

Anz

have axes oriented

indicative

of

northeast

88

compression. During the Oligocene or earliest Miocene, regime

changed

to one of

northeast

the stress

extension.

resulted in an episode of northeast tilting,

This

and the

reactivation of the early northwest strike-slip fault set as west-down normal faults.

Some form of regional tilting

associated with this period of

fault reactivation is

implied by the predominant southwest dip of the faults as presently exposed.

The early strike-slip faults would

normally have developed vertically;

requiring tilting

either prior to or during reactivation to reach their present orientations.

Dip-slip movement on these

northwest-trending faults resulted in substantial tilting and

down

faulting

of

isolated

blocks

of

platform

sediments, and the emplacement of these blocks as inliers within the Precambrian basement.

Erosion during this

period stripped the uplifted areas of

their sediment

cover, leaving the Precambrian exposed in all areas except the down-faulted inliers.

89

Red Sea Coastal Plain Sediments Gebel el Rusas Formation.

The middle Miocene Gebel el

Rusas Formation has a highly irregular outcrop pattern, with abrupt

lateral

f acies variations reflecting the

irregular topography of the original Miocene basin edge, now exhumed due to a combination of marginal uplift, basin subsidence, and/or sea leve 1 fal 1.

It occurs in three

distinct structural settings within the study area (fig. 2 5) :

1. as a large barrier reef development on a local horst block (the Ambagi reef), 2. as fringing reefs developed against a fault scarp of

the

Precambrian

basement

(the

Rusas/

Precambrian reefs), and 3. as a reefal cap on exposed platform sediments (the Isewid reef). Ambagi Reef.

The Ambagi reef is an excellent example

of the interaction of sedimentation, sea level changes.

local tectonics and

It is located at the north end of the

Gihania valley, on the north bank of Wadi Ambagi, and is visible Quseir.

just north of the main highway,

7 km west of

It formed along the south side of

a

marked

indentation in the Miocene coastline (fig. 26), associated with an area presently bounded by Wadi Ambagi and Wadi

90

·~G' RED SEA

26'05'

\

- ' \ I

....., '1

/'

I•

' I

/

\

--

1km 34'15'

Figure 25. Coastal plain reef complexes, with cross section locations.

~

N

91

\

\

RED SEA -0

"6'

.

..1'6>

,,_..

0

Quseir ·

'-/ ,,,

\___

~. o..r_... :.,,:.

/

\

\

~15)

I' '\

I --

--

\

/

Figure 26. Map showing Red Sea coastline during middle Miocene time.

92

Quseir el Qudeim.

The reef complex is developed on a

substrate of chaotic Thebes Formation,

with numerous

disturbed blocks and slump structures indicating highly active local faulting. The exposure of the Ambagi reef complex (fig. 27) is steep on all

sides,

and

with

the

adjacent Evaporite

Formation stands as a prominent topographic high above the surrounding coastal plain.

Two capping reef terraces (the

main reef and upper reef members) are flat, undeformed, and dip approximately 2° to the northeast.

Coarse

Precambrian-derived pebble conglomerates form an off-block equivalent to the upper reef member north of the reef complex, while local outcrops of thin-bedded to massive gypsum of the late Miocene Evaporite Formation overlie the reef plateau.

Individual units within the reef complex

dip steeply and thicken dramatically off the east and northeast edges of

the block,

indicating substantial

synsedimentary faulting. The underlying structure of the Ambagi reef is an uplifted horst block developed within a zone of coastal flexure.

The horst is formed by the interaction of a

major flexure zone parallel to the Red Sea with a zone of west-northwest faults,

possibly related to the old

Precambrian structural grain (fig. 28).

The interaction

UNITS

~

Quaternary Sediments

·40 000 years

(Brown, 1970) is well developed along much of the northern Arabian

shoreline.

The

underforrned

nature

of

these

terraces and their regional distribution indicate that the Quaternary history of the northern Red Sea region has been characterized by relatively little local deformation.

form regional uplift,

with

This regional uplift may be due

139

to increased heat flow in the region as active oceanic spreading progresses northward from centra 1 Red Sea.

the southern and

C H A P T E R

V I I

GEOLOGIC HISTORY OF THE QUSEIR AREA Precambrian Geologic History

The Precambrian evolution of the Ambagi area began with the deposition of a thick sequence of interbedded volcanic and volcanogenic sedimentary rocks (table 2). The depositional environment of this group of rock units

was

characterized

by

varied

terrain,

rapid

deposition, both subaerial and subaqueous depositional sites, high topographic relief, and numerous local sources of

volcanic

and

sedimentary

characteristics are

typical

of

material.

an oceanic

These

island-arc

complex. The deposition of these volcano-sedimentary units was followed by an extended period of orogeny, during which the entire region was deformed and metamorphosed to lower greensch

t f

es.

The orogeny included a phase of major

northeast regional compression which resulted in: 1.

the folding

sode that produced the el Isewid

synform, 2.

the development of a regional foliation, and

3.

northwest

regional

extension,

including

the

emplacement of a set of northeast trending quartz veins perpendicular to the extension direction. 140

141

Table 2.

Precambrian History of the Quseir Area

Lithologic Units

Orogenic Events

Tectonic Setting

Metavolcanic/Metasedimentarv Group 1. deposition of volcanic and volcanogenic sedimentary units (vm, vp, sv, vs, sf, vf, sc, vi, vw, sp, ss)

1. minor syndepositional faulting and metasomatism.

Oceanic Island Arc

Period of Main Orogeny Subvolcanic/Plutonic

~

2. intrusion of mafic dikes(?) 3. intrusion of Older Granite ( og) 4. intrusion of Post~amrnamat Felsite (ph) ~.

intrusion of Younger Granites (yg) al Gebel Arnbagi granodiorite o) southwest granite c) southeast alkali granite

6. intrusion of felsic dikes

2. major NE directed compression results in: a) regional folding to produce the el Isewid synform b) development of regional foliation c) NW extension and emplacement of quartz veins perpendicular to sigma 3 3. pervasive lower greenschist facies regional metamorphism 4. development of crosscutting fracture cleavage sets 5. continued faulting and minor folding deforms foliation and fracture cleavage

Arc/ Continent Collision

Cratonization

142

Major faulting episodes probably also occurred during this period.

The orogeny may have resulted from some form of

collision between the early island arc complex and the African craton. During and immediatly following the main orogeny, the members of the subvolcanic/plutonic group were intruded into the deformed volcano-sedimentary pile.

Tonalite of

the Older Granites series was probably emplaced during the main orogeny,

whereas rhyolite porphyry of the Post-

Hammamat Felsites (ph) and granodiorite to alkali granite of the Younger Granite series were late to post-tectonic intrusions.

This period of increasingly fractionated

granitic intrusion may represent the final cratonization

of

the

region

following

stages of

arc-continent

collision.

Phanerozoic Geologic History Erosion of Precambrian.

The Quseir area was tectonically

stable during most of the early Phanerozoic, by a

regional

peneplain which is developed on the

Precambrian basement (table 3). by a saproli

as indicated

c horizon,

The peneplain is overlain

forming the flat,

low-relief

surface upon which the Cretaceous to Eocene platform sediments were deposited.

Some Paleozoic or early

Table 3.

Phanerozoic History of the Quseir Area

Tectonic Phase

Time Period

Erosion of Precambrian

Cambrian to middle Cretaceous

Units Deposited 1. kaolinized saprolitic horizon

Tectonic Events 1. epeirogenic uplift, erosion, and peneplaination of the Precambrian basement

2. possibly some Paleozoic sediments, subsequently eroded Platform Sediment Deposition

middle Cretaceous to middle Eocene

3. deposition of the platform sediments sequence: a) Nubia Fm. b) Quseir Fm. c) Duwi Fm. d) Dakhla Fm. e) Tarawan Chalk f) Esna Shale g) Thebes Fm.

2. epeirogenic downwarping, and a progressive north to south marine transgression from the Tethys Sea 3. epeirogenic uplift and/or lower sea level results in marine regression and end of deposition in middle Eocene.

..,..

f-'

I,;.)

Table 3. Tectonic Phase

NorthNortheast Compression

Phanerozoic History of the Quseir Area (page 2) Time I Units Period Deposited

middle Eocene to late Oligocene

Tectonic Events

4. north-northeast regional compression results in development of a conjugate system of N to NW trending right lateral faults, and NE trending left lateral faults 5. broad folds (e.g. Gebel Anz) in the platform sediments may also have formed during this period

Continental Margin Extension

early Miocene

6. development of a NE extensional stress regime

4. deposition of Nakheil Fm. in fault-bounded depressions

5. development of a terminal erosion surf ace, the mid-Tertiary pediplain

7. reactivation of strike-slip faults as west dipping normal faults

8. emplacement of down faulted platform sediment blocks (e.g. Gebel Atshan, Gihania) in asymetric grabens in the Precambrian basement

9. uplift in coastal region combined with differential subsidence results in erosion of platform sediments cover from topographic highs

..,.. ..,..

I-'

Table 3. Tectonic Phase

Phanerozoic History of the Quseir Area (page 3) Time Period

Units Deposited

Tectonic Events

Formation of Proto Red Sea

middle Miocene

6. deposition of Gebel el Rusas Fm. in the developing Red Sea basin

10. continued regional extension, down faulting, and possibly sea floor spreading results in development of Red Sea marine basin

Quiescence

late Miocene

7. deposition of Evaporite Fm. in Red Sea basin

11. hiatus of tectonic activity

Sea Floor Spreading

Pliocene to Present

8. deposition of Gasus Fm.

12. beginning (or resumption?) of sea floor spreading in Red Sea 14. minor block faulting and flow of underlying gypsum results in seaward tilting of the coastal plain sediments

9. deposition of wadi sediment and reef terraces

13. second phase of coastal uplift begins, and continues to present I-'

+:-

ln

146

Mesozoic units may have been present, but if so these have been subsequently eroded away, and the superposition of middle

Cretaceous

Nubia

Formation

on

peneplained

Precambrian basement indicates relative tectonic stability for this entire period. Epeirogenic downwarping in

Platform Sediment Deposition.

the middle Cretaceous resulted in a north to south transgression of the Tethys Sea and the deposition of a widespread and uniform sequence of platform sediments across the region.

Fluvial and f luvio/deltaic sands of

the middle Cretaceous Nubia Formation are overlain by littoral and shallow marine shelf sediments, in the Thebes limestone of lower Eocene age. extent

of

these

stratigraphic

units,

and

similarities,

their

culminating The regional

lithologic

indicates

that

no

and

major

tectonic activity occurred during the period of their deposition. North-Northeast Compression.

During the period from

middle Eocene to late Oligocene,

a north-northeast

compressional stress regime developed, resulting in the formation of a conjugate system of north- to northwesttrending right-lateral strike-slip faults,

and northeast-

trending left-lateral strike-slip faults.

Broad folds in

147

the platform sediments (e.g., formed during this period. this

system appear

Gebel Anz) may also have

Northeast-trending faults of

to have been affected by earlier

Precambrian trends averaging N60E,

and together these

structural elements may have played a

role in the

subsequent localization of transform faults in the Red Sea rift.

This fault system cuts the Thebes Formation and all

older units,

but does not affect the Miocene and later

sediments related to the Red Sea, thus bracketing the age of the stress system as post-lower Eocene and pre-Miocene. Continental Margin Extension.

In the early Miocene, a

regional northeast extensional stress regime developed. This resulted in the reactivation of strike-slip faults as west-dipping normal faults,

and the emplacement of down-

faulted platform sediment blocks (e.g.,

Gihania and Gebel

Atshan) in asymmetric grabens in the Precambrian basement. Characteristic of this period was extensive block tilting toward the evolving rift valley, possibly as a result of a loss of lateral support as the crust in the vicinity of the rift was thinned and extended.

Contemporaneous uplift

of the rift margins, possibly due to increased heat flow in the vicinity of the active rift, resulted in rapid erosion of the platform sediments from topographic highs in the Precambrian basement.

Sediments derived from this

148

period of

rapid erosion

deposited

in

depressions,

local

were

the

downwarps

Nakheil and

Formation,

fault-bounded

and voluminous sediments probably deposited

as coarse red beds in the evolving rift valley. of

the rift

marginal

fault

blocks

ter~inal

development of a flat

Erosion

culminated

erosion surface,

in

the

the mid-

Tertiary pediplain. Formation of

the

£ro~o

Red Sea.

During the middle

Miocene, continued regional extension, normal faulting and/or sea-floor spreading resulted in subsidence to east and the formation of the Red Sea marine basin.

the Sea-

floor spreading may have begun during this first phase of extension, been

or the continuing regional extension may have

accommodated

by

listric

normal

faulting,

subsidence, and thinning of the continental crust. first unit deposited on the margin of

block The

the developing

basin was the middle Miocene Gebel el Rusas Formation. The basal member of this formation,

a coarse Precambrian

derived-conglomerate, is deposited directly on stripped Precambrian basement and highly eroded or down-faulted platform sediment blocks. Quiescence.

Miocene

A hiatus of tectonic activity during the late

indicates

a

relaxation

extensional stress regime.

of

the

northeast

During this period the Red Sea

149

became hypersaline, and a thick sequence of evaporites, the Evaporite Formation, was deposited. Sea floor spreading.

A second phase of extension at the

beginning of the Pliocene resulted in the initiation (or resumption?) of sea floor spreading in the Red Sea basin. This coincided with a

second phase of coastal uplift

and/or basin subsidence, the connection of the Red Sea basin to the Indian Ocean, and a return to normal marine conditions of sedimentation with the deposition of the Gasus Formation. underlying

Minor block faulting and flow of the

Evaporite

Formation

in

the

coastal

plain

resulted in northeast tilting and the development of northeast sediments.

transverse

highs

within

the

coastal

plain

Pleistocene to Recent wadi and reef terraces

have developed as a result of continued uplift of the coastal plain.

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159

Youssef, M. I., 1957, Upper Cretaceous rocks in Kosseir area: Bull. Inst. Desert Egypte, t. 7, no. 2, p. 35-

53. Zak,

I., and Freund, R., 1981, Asymmetry and basin migration in the Dead Sea Rift: Tectonophysics, v. 80, no. 1-4, p. 27-38.

PLATE

34°10'

PRECAMBRIAN GEOLOGIC MAP OF THE QUSEIR AREA, RED SEA COAS~ EGYPT

RED 1

0

2

3

SEA

Kilometers

EXPLANATION Scale

=

1:40 000

?s

Phanerozoic Sediments Subvolcanic/Plutonic Group Younger Granite Post-Hamrnarnat Felsite Older Granite GI h an I 11

Metavolcanic/Metasedimentary Group

z